The area between axis and line are commonly emphasized with colors, textures and hatchings.
His book The Commercial and Political Atlas, published in 1786, contained a number of time-series graphs, including Interest of the National Debt from the Revolution and Chart of all the Imports and Exports to and from England from the Year 1700 to 1782 that are often described as the first area charts in history.
[1][2] Area charts are used to represent cumulated totals using numbers or percentages (stacked area charts in this case) over time.
Use the area chart for showing trends over time among related attributes.
Area charts which use vertical and horizontal lines to connect the data points in a series forming a step-like progression are called step-area charts.